Titanium-containing materials

ABSTRACT

The invention relates to a method of preparing a solution containing colloidal particles which contain crystalline titanium dioxide wherein one or more hydrolysable titanium-containing compound(s) is stabilised by oxalic acid in a reaction medium.  
     The reaction further relates to the preparation of titania materials (including particulate materials, coating solutions and films) which comprise or include anatase phase titania, and so are suitable in photocatalytic applications.  
     The invention also deals with a method of preparing B-phase titania.

FIELD OF THE INVENTION

[0001] This invention relates to processes for preparingtitanium-containing materials. More particularly, it relates toprocesses of preparing solutions containing colloidal particlescontaining titanium ions, and to processes for preparing titaniumdioxide containing materials from such solutions. This invention alsorelates to application of these titanium-containing materials.

BACKGROUND OF THE INVENTION

[0002] Titanium-containing composite materials have a range ofapplications. These include applications that depend on the ability ofthese materials to function as photocatalysts, constituents of filmelectrodes, hydrophilic surfaces, and to prevent the growth ofmicro-organisms.

[0003] Photocatalysts

[0004] Photocatalysis using titania and titania-based materials havebeen widely described in recent years for water treatment and airpurification (Hoffmann, Martin, Choi and Bahnemann, Chem. Rev. 1995, 95,69). Anatase was reported to be the most active phase of TiO₂ with aband gap of 3.2 eV (387 nm). Trace organic contaminants can bephotodegraded on the surface of anatase particles under UV light tocarbon dioxide, water, and possibly mineral ions.

[0005] Different factors have been reported to affect the photoactivityof anatase. High surface area and large pore diameter are extremelyimportant to enhance the adsorption of contaminants and increase thelight interaction with the material.

[0006] The crystallite size can also determine the extent ofphotoactivity of TiO₂. Smaller crystallite size is considered essentialto repress charge recombination of the photogenerated electrons andholes and render them more available for redox reactions at the surfaceof the photocatalyst particles.

[0007] Another way of increasing the photoactivity of anatase is bydoping with metals or metal oxides. Of the metals, platinum doping hasbeen found to be very effective in improving the photocatalytic process.The extent of doping and the dopant particle size are important factors.Doping a photocatalyst with more than 5% by weight platinum should beavoided as this could produce large platinum particle size and preventthe light from reaching the photocatalyst surface. Deposition ofplatinum metal on titania has been reported using a number of differentmethods. One of the methods is by photodeposition of platinum byirradiating hexachloroplatinic acid that is adsorbed on anatase powderunder nitrogen first described by Kraeutler and Bard (J. Am. Chem. Soc.1978, 100, 4317). Photodeposition of platinum was also achieved byilluminating a deaerated suspension of hexachloroplatinic acid and TiO₂using ethanol as a sacrificial electron donor (Yamaguchi and Sato, J.Chem. Soc. Faraday Trans. 1, 1985, 81, 1237). High temperature reduction(480° C.) of hexachloroplatinic acid adsorbed on TiO₂ in hydrogen gaswas also reported (Pichat et al Nouv. J. Chim 1981, 5, 627636). Andersonand Xianzhi (Patent number WO9640430, 1996) described a method ofreducing hexachloroplatinic acid adsorbed on TiO₂ pellets using NaBH₄ indilute NaOH.

[0008] Doping of TiO₂ with silver by photodeposition is known (Schwarzet al, Chem. Rev. 1995, 95, 477) where TiO₂ was dispersed in a dilutesolution of silver nitrate and a sacrificial agent. The suspension wasthen irradiated with a mercury lamp. However copper 2+ was reported tobe reduced to Cu₂O under irradiation of TiO₂ (Sakata et al, Chem.Letters, 1998, 1253).

[0009] The formation of photocatalyst thin films has been reported to beuseful in maintaining clean surfaces. Building surfaces like windows andtiles, automobile screens and mirrors, etc. may attract all sorts ofcontaminants such as oil deposits, smoke and dust. When a surface iscoated with a photocatalyst film, this coating can degrade the depositedcontaminants by the aid of natural or artificial UV light. This processof phenomenon is usually referred to as a “self-cleaning surface”.

[0010] Hydrophilic Surfaces

[0011] Windows, mirrors and other surfaces are fogged when cold due tothe condensation of moisture droplets. One of the ways to avoid thisphenomenon is to make the surface hydrophilic by applying a transparenthydrophilic coating, such as TiO₂. Hydrophilicity can be expressed bymeasuring the contact angle of a water drop on the surface. In order tomaintain the hydrophilicity of such a surface, it needs to beperiodically exposed to a UV light. Exposure to even a low intensity ofUV radiation from sunlight or fluorescent light can maintain thehydrophilicity. In this way the contact angle can be reduced to 2-5°,which is enough to prevent fogging of the surface. A recent Patent byTOTO Ltd (EP 0816466 A1, 1998) described a method of applyingTiO₂-containing thin film that is capable of maintaining a contact angleof 3° when subjected to irradiation using a white fluorescent lamphaving a UV intensity of 0.004 mW/cm².

[0012] Scrubbing Technology

[0013] One of the desired applications of photocatalysts is their use todegrade volatile organic compounds (VOCs) under UV irradiation. ManyVOCs such as formaldehyde, toluene trichloroethylene (TCE), ethylene,etc. are considered toxic, carcinogenic, irritant or harmful to adifferent extent. Some of these are considered easy to photodegrade suchas formaldehyde, while others, such as toluene and ethylene, areconsidered difficult to decompose. Photocatalysts can also be used inpurification of water to degrade any traces of pollutants such asorganic compounds, dyes, etc., and even microorganisms by allowing waterto be in contact with the UV irradiated photocatalyst.

[0014] Of particular interest is the effect of ethylene gas on storedfruit, vegetables and cut flowers. These produce need to be consumed,exported or delivered to supermarkets and food stores while still beingfresh. Ageing of produce can be caused by exposure to ethylene gas. Thisis known to be released by produce, such as apples and bananas and willaffect other things that are stored in the same place. Ethylene is aplant hormone that causes ripening and ageing of fruit, vegetable andflowers even in low concentrations. The ripening speed may vary from onetype of produce to another depending on the concentration of ethylene.For example, tomatoes ripen within hours if exposed to ethylene in aconcentration of more than 100 ppm. Kiwi fruit may ripen even at lowerconcentration of few parts per million of ethylene. This can createproblems in storing or transporting different produce in the same coldstore or container.

[0015] Nelson et al (U.S. Pat. No. 6,240,767, 2001) have described asystem for accurately monitoring part per million level of ethylene gasin atmosphere and fruit containers. Having an efficient way to controland degrade high level of ethylene is as important as monitoring theethylene concentration during storage or transport.

[0016] Patterned Films

[0017] The development of new methods for depositing patterned ceramicfilms onto surfaces is especially important in microcircuit fabricationsuch as field-effect transistors that need to be down-sized to asubmicrometer thickness. Titanium dioxide has a favourable dielectricand refractory properties to be utilised as part of a micropatternedfilm. Koumoto, Sugiyama and Seo (Chem. Mater. 1999, 11, 2305) havedescribed a low temperature patterning process for TiO₂ deposition thatutilises phenyltrichlorosilane as a patterning template which wasirradiated with a Hg lamp through a photomask before deposition of TiO₂from acidic (NH₄)₂TiF₆ solution. These patterns exhibit significant lineedge roughness of ˜7.3 micrometer that corresponds to 28% variationaccording to the authors, which exceeds the usual 5% variation allowedby current electronics design rules. Kikuta, Tkagi and Hirano (J. Am.Ceram. Soc. 1999, 82, 1569) have shown that finer patterns of TiO₂ canbe produced from solutions of titanium alkoxide modified withalkanolamines by photolithography. The precursors were coated on asubstrate and decomposed by ultra-high-pressure mercury lamp. The filmswere then heat-treated to convert it to anatase phase.

[0018] It is an object of the present invention to provide analternative process for preparing titanium-containing materials, and/orto provide an alternative means of employing titanium containingcompounds, and/or to at least provide the public with a usefulalternative.

STATEMENTS OF THE INVENTION

[0019] In a first aspect of the invention there is provided a method ofpreparing a solution containing colloidal particles which containtitanium ions comprising or including the step of:

[0020] A. reacting or otherwise stablilising one or more hydrolysabletitanium-containing compound(s) with oxalic acid in a reaction mediumunder conditions such that a colloidal solution is obtained.

[0021] Preferably A occurs under conditions such that peptization of thecolloidal solution is substantially obtained and substantiallymaintained.

[0022] Preferably the conditions include stirring or agitation of theone or more hydrolysable titanium-containing compound(s) with oxalicacid in the reaction medium, more preferably at a temperature betweenambient temperature to near the boiling point of the reaction mixture,even more preferably at a temperature between about 40° C. and about 80°C. Preferably the stirring or agitation occurs over a reaction timeranging from substantially 15 minutes up to substantially 3 hours.

[0023] Preferably the reaction medium comprises water or a water/alcoholmixture and wherein the titanium-containing compound is hydrolysable inwater and/or in base.

[0024] Preferably the titanium containing compound is water-hydrolysableand the titanium-containing compound is of the formula Ti(OR)₄, where Ris a C₂-C₆ linear or branched chain alkyl group; more preferably thetitanium containing compound is titanium tetraisopropoxide and/ortitanium tetrabutoxide.

[0025] Preferably the water-hydrolysable titanium containing compoundis:

[0026] first combined with a solution of oxalic acid in alcohol,followed by addition of water, or

[0027] added directly to water, or to a mixture of water and an alcohol,to form a slurry, followed by addition of oxalic acid, or

[0028] added to a solution of oxalic acid in water or in a mixture ofwater and alcohol.

[0029] Preferably the water-hydrolysable titanium-containing compound ishydrolysed using water prior to reaction with or stabilisation by oxalicacid, to give a hydrolysis product.

[0030] Alternatively or additionally the titanium-containing compound isbase-hydrolysable and the titanium-containing compound is selected from,but not restricted to, TiCl₄ and/or TiOSO₄.

[0031] Preferably the base-hydrolysable titanium-containing compound ishydrolysed to a hydrolysis product, using a base prior to reaction withor stabilisation by oxalic acid, the hydrolysis product being filteredand/or washed, to form a slurry before reaction with or stabilisationby, the oxalic acid.

[0032] Preferably the oxalic acid is either anhydrous oxalic acid, orhydrated oxalic acid, and preferably the amount of oxalic acid is suchas to provide a mole ratio of oxalic acid:titanium in the range of about0.2:1 to about 1:1.

[0033] Preferably the water content of the reaction medium is such as toprovide a mole ratio of water:titanium in the range of from about 200:1to about 800:1; more preferably in the range of from about 400:1 toabout 600:1.

[0034] Preferably, when alcohol is present in the reaction medium, thealcohol is a mono hydroxyl aliphatic alcohol having the formula ROH,where R is a C₁ to C₄ linear or branched alkyl group, such as ethanol ort-butanol, and the preferred amount of alcohol present is such as toprovide a mole ratio of alcohol:titanium of from zero to 100:1, morepreferably 10:1 to 50:1.

[0035] Preferably the solution may be stored at any concentration levelprior to further use, preferably at up to about 32% by weight TiO₂,between 0° C. and 20° C.

[0036] Preferably the oxalate concentration of the solution is at anystage reduced by irradiating the solution with UV light.

[0037] According to a second aspect of the invention there is provided asolution containing colloidal particles which contain titanium ionsprepared substantially according to the preceding method.

[0038] In a third aspect of the invention there is provided a method ofpreparing a solution containing colloidal particles which containcrystalline titanium dioxide comprising or including the step of:

[0039] A. reacting or otherwise stabilising one or more hydrolysabletitanium-containing compound(s) with oxalic acid in a reaction mediumunder conditions such that a colloidal solution is obtained.

[0040] Preferably A occurs under conditions such that peptization of thecolloidal solution is substantially obtained and substantiallymaintained.

[0041] Preferably the conditions include stirring or agitation of theone or more hydrolysable titanium-containing compound(s) with oxalicacid in the reaction medium, more preferably at a temperature betweenambient temperature to near the boiling point of the reaction mixture,even more preferably at a temperature between about 40° C. and about 80°C. Preferably the stirring or agitation occurs over a reaction timeranging from substantially 15 minutes up to substantially 3 hours.

[0042] Preferably the reaction medium comprises water or a water/alcoholmixture and wherein the titanium-containing compound is hydrolysable inwater and/or in base.

[0043] Preferably the titanium containing compound is water-hydrolysableand the titanium-containing compound is of the formula Ti(OR)₄, where Ris a C₂-C₆ linear or branched chain alkyl group; more preferably thetitanium containing compound is titanium tetraisopropoxide and/ortitanium tetrabutoxide.

[0044] Preferably the water-hydrolysable titanium containing compoundis:

[0045] first combined with a solution of oxalic acid in alcohol,followed by addition of water, or

[0046] added directly to water, or to a mixture of water and an alcohol,to form a slurry, followed by addition of oxalic acid, or

[0047] added to a solution of oxalic acid in water or in a mixture ofwater and alcohol.

[0048] Preferably the water-hydrolysable titanium-containing compound ishydrolysed using water prior to reaction with or stabilisation by oxalicacid, to give a hydrolysis product.

[0049] Alternatively or additionally the titanium-containing compound isbase-hydrolysable and the titanium-containing compound is selected from,but not restricted to, TiCl₄ and/or TiOSO₄.

[0050] Preferably the base-hydrolysable titanium-containing compound ishydrolysed to a hydrolysis product, using a base prior to reaction withor stabilisation by oxalic acid, the hydrolysis product being filteredand/or washed, to form a slurry before reaction with or stabilisationby, the oxalic acid.

[0051] Preferably the oxalic acid is either anhydrous oxalic acid, orhydrated oxalic acid, and preferably the amount of oxalic acid is suchas to provide a mole ratio of oxalic acid:titanium in the range of about0.2:1 to about 1:1.

[0052] Preferably the water content of the reaction medium is such as toprovide a mole ratio of water:titanium in the range of from about 200:1to about 800:1; more preferably in the range of from about 400:1 toabout 600:1.

[0053] Preferably, when alcohol is present in the reaction medium, thealcohol is a mono hydroxyl aliphatic alcohol having the formula ROH,where R is a C₁ to C₄ linear or branched alkyl group, such as ethanol ort-butanol, and the preferred amount of alcohol present is such as toprovide a mole ratio of alcohol:titanium of from zero to 100:1, morepreferably 10:1 to 50:1.

[0054] Preferably the solution may be stored at any concentration levelprior to further use, preferably at up to about 32% by weight TiO₂,between 0° C. and 20° C.

[0055] Preferably the oxalate concentration of the solution is at anystage reduced by irradiating the solution with UV light.

[0056] According to a fourth aspect of the invention there is provided asolution containing colloidal particles which contain crystallinetitanium dioxide prepared substantially as herein described withreference to any one of more of the accompanying examples.

[0057] According to a fifth aspect of the invention there is provided amethod of preparing a TiO₂-Containing Product comprising or includingthe steps of:

[0058] I. preparation of a solution containing colloidal particles whichcontain crystalline titanium dioxide wherein the particles arestabilised by oxalic acid, or stabilised by reaction with oxalic acid,and

[0059] II. further processing of the solution to obtain the product.

[0060] Preferably I occurs under conditions such that peptization of thecolloidal solution is substantially obtained and substantiallymaintained.

[0061] Preferably the conditions include stirring or agitation of one ormore hydrolysable titanium-containing compound(s) with oxalic acid in awater or water/alcohol reaction medium, more preferably at a temperaturebetween ambient temperature to near the boiling point of the reactionmixture, even more preferably at a temperature between about 40° C. andabout 80° C. Preferably the stirring or agitation occurs over a reactiontime ranging from substantially 15 minutes up to substantially 3 hours.

[0062] Preferably the TiO₂ phase in the product, at least initially,includes, is predominantly or is substantially anatase.

[0063] Preferably the method comprises or includes the steps of:

[0064] 1) preparation of a solution containing colloidal particles whichcontain titanium ions wherein the particles are stabilised by oxalicacid or stabilised by having been reacted with oxalic acid, and

[0065] 2) preparation of a colloidal mixture by addition of, or mixingwith, one or more additives to the solution, and

[0066] 3) further processing of the solution to obtain the product.

[0067] Preferably step 1) comprises or includes the method as previouslydescribed in one or more of the first-fourth aspects of the invention.

[0068] Preferably the additives of step 2) include one or more of:

[0069] a) silica or a silica precursor, (preferably when added it is ascolloidal silica, and preferably added in an amount to yield a ratiosubstantially from 1 to 99 wt % relative to titanium in the product,more preferably from 30-60 wt %, and preferably the concentration of thecolloidal silica is such as to provide between about 1 and 50% by weightin the product),

[0070] b) water, or alcohol, soluble ketone(s)

[0071] c) organic acid(s),

[0072] d) water soluble aliphatic or aromatic alcohol(s), diol(s) orpolyol(s),

[0073] e) elhanolamine(s),

[0074] f) metal precursor(s),

[0075] g) surfactant(s) (and preferably when added the surfactant(s) isor includes one or more of the Brij series, Triton series, Tergitolseries, Pluronic series, potassium dodecyl sulphate, or any othersurfactant that does not cause gelling),

[0076] h) silane(s) (and preferably when added, it is is added neat oras solution in an aqueous or organic solvent that is miscible withwater, preferably it is a hydrolysable or partially hydrolysable silanecompound of a formula RSiX₃, R₂SiX₂ and SiX₄ (where R is a simple orfunctionalised organic group and X could be a halide or an alkoxidegroup)).

[0077] Preferably if added, the metal precursor is a metal salt or metalcomplex, more preferably a soluble metal salt or complex, preferably ofPd, Pt, Ag and Cu.

[0078] When the metal is Pd or Pt preferably the precursor is (but notrestricted to) one of the hexachloro-complexes of Pd or Pt, andpreferably the Pd or Pt hexachloro-complex is mixed with a low carbonorganic compound (such as formaldehyde, formic acid, methanol orethanol) as a sacrificial compound, which is preferably added in excessrelative to the precursor metal, more preferably at a etal:sacrificialcompound mole ratio of approximately.1:5.

[0079] Alternatively or additionally, the metal is Ag and the precursoris one or more of (but not restricted to) silver acetate or silvernitrate.

[0080] Alternatively or additionally the metal is Cu and the precursoris one or more of (but not restricted to) copper acetate, coppersulphate and copper nitrate.

[0081] Preferably step 3) includes removal of the solvent, morepreferably by one or both of the steps of:

[0082] i) causing the solution to gel (a gelling step),

[0083] ii) curing of the gel (a curing step) to remove or reduce thequantity of the oxalic acid and/or any one or more additives.

[0084] Preferably the gelling step is effected by one or more of:

[0085] evaporating the solvent; at room temperature or above; and/or

[0086] evaporating the solvent under a vacuum, with or without heating;and/or

[0087] addition of a gelling agent including (but not restricted to) adilute mineral acid solution such as of HCl, HNO₃ or H₂SO₄, or analkaline solution such as KOH, ammonia, sodium carbonate ortetraalkylammonium hydroxide.

[0088] Preferably a xerogel may be produced from the gelling step.

[0089] Preferably the curing of the gel is effected by exposure to UVradiation and/or by heat.

[0090] Preferably the wavelength of the UV radiation substantially orpartially coincides with the band gap of the TiO₂ in the anatase phase.

[0091] Preferably the curing time is determined by the amount of oxalicacid to be decomposed and/or the wavelength of the radiation and/or theintensity of the radiation.

[0092] Preferably there is an additional step 4), which includes one orboth the steps of:

[0093] i) impregnation of the titanium containing-product with a metalprecursor, (an impregnation step) and/or

[0094] ii) transformation to a metal or metal oxide of any metalprecursor added within step 2) and/or step 4) (a transformation step).

[0095] Preferably the metal of the precursor of i) may be one or more ofPd, Pt, Cu or Ag.

[0096] Preferably when the metal precursor includes Pd or Pt the metalprecursor may be mixed with a sacrificial compound of formaldehyde,formic acid, methanol or ethanol, in excess relative to the metalrecursor.

[0097] Preferably the transformation step occurs by one or more of:

[0098] i) heating at a suitable temperature to transform the metalprecursor to the metal or metal oxide, and/or

[0099] ii) exposing the metal precursor or the TiO₂-Containing Productcontaining the metal precursor, to a dilute hydrazine hydrate solutionfor a sufficient time to allow the complete reduction of the metal tozero valency, and/or

[0100] iii) UV irradiation to form metal particles and/or metal oxideswithin the titanium dioxide.

[0101] Preferably when:

[0102] the metal of the metal precursor is Ag, UV irradiation isemployed and UV irradiation is stopped substantially when the colour ofthe TiO₂-product changes to light grey-black, and/or

[0103] the metal of the metal precursor is Cu, UV irradiation isemployed and UV irradiation is stopped substantially when the colour ofthe TiO₂-Containing Product changes from light green to bronze, and/or

[0104] the metal of the metal precursor is Pd, UV irradiation isemployed and UV irradiation is stopped substantially when the colour ofthe TiO₂-Containing Product changes from grey to black and/or

[0105] the metal of the metal precursor is Pt, UV irradiation isemployed and UV irradiation is stopped substantially when the colour ofthe TiO₂-Containing Product changes from grey to black.

[0106] Preferably when hydrazine hydrate solution exposure is employedin the transformation step the TiO₂-product is then washed with water toremove the excess hydrazine.

[0107] Preferably the final metal content in the TiO₂ of theTiO₂-product is less than 2% by weight, more preferably it is between0.2 to 0.5% by weight.

[0108] Preferably sometime prior to step 3) the oxalate concentration ofthe solution is reduced by irradiating the solution with UV light.

[0109] Preferably the product is particulate in nature; more preferablythe product is a powder; alternatively it is granular.

[0110] According to a sixth aspect of the invention there is provided amethod of preparing a TiO₂ coating solution comprising or including thesteps of:

[0111] I. preparation of a solution containing colloidal particles whichcontain crystalline titanium dioxide wherein the particles arestabilised by oxalic acid, or are stabilised by having been reacted withoxalic acid, and

[0112] II. further processing of the solution to obtain the coatingsolution.

[0113] Preferably I. occurs under conditions such that peptization ofthe colloidal solution is substantially obtained and substantiallymaintained.

[0114] Preferably the conditions include stirring or agitation of one ormore hydrolysable titanium-containing compound(s) with oxalic acid in awater or water/alcohol reaction medium, more preferably at a temperaturebetween ambient temperature to near the boiling point of the reactionmixture, even more preferably at a temperature between about 40° C. andabout 80° C. Preferably the stirring or agitation occurs over a reactiontime ranging from substantially 15 minutes up to substantially 3 hours.

[0115] Preferably the method comprises or includes the steps of:

[0116] 1) preparation of a solution containing colloidal particles whichcontain crystalline titanium dioxide wherein the particles arestabilised by oxalic acid, or are stabilised by having been reacted withoxalic acid,

[0117] 2) preparation of a colloidal mixture by addition of one or moreadditives to the solution.

[0118] Preferably step 1) includes or comprises the method as claimed inany one of the first to fourth aspects of the invention.

[0119] Preferably step 2) includes any one or more of the following:

[0120] i) Addition of or mixing with silica, or a silica precursor(preferably, when added or mixed, it is colloidal silica, and it isadded in an amount to give a ratio substantially between 1 and 99 weightpercent relative to titanium, more preferably from 30 to 60 wt %relative to titanium; and preferably the concentration of the colloidalsilica is between about 1 and 50% by weight),

[0121] ii) Addition of or mixing with any proportion of water-soluble oralcohol-soluble ketone(s) (preferably when added or mixed, it is acetoneand/or acetylacetone),

[0122] iii) Addition of or mixing with any proportion of organic acid(s)(preferably when added or mixed, and it is mono-, di- ormulti-functional, with or without hydroxyl groups, more preferablyit/they may be one or more of acetic, lactic, tartaric, citric, maleic,malic, malonic, diglycolic, benzoic, 1,2,4,5-C₆H₂ (COOH)₄, EDTA, and/ormixtures thereof),

[0123] iv) Addition of or mixing with any proportion of water-solublealiphatic or aromatic alcohol(s), diol(s) or polyol(s) (preferably whenadded it/they may be one or more of ethanol, propanol, ethylene glycol,glycerol, polyethylene glycol, polyvinylalcohol, phenol, catechol,polysaccharides),

[0124] v) Addition of or mixing with any proportion of ethanolamine(s),(such as monoethanolamine, diethanolamine and triethanolamine, or amixture thereof),

[0125] vi) Addition of or mixing with any proportion of surfactant(s)(preferably when added or mixed, it/they may be selected from one ormore of the Brij series, Triton series, Tergitol series, Pluronicseries, potassium dodecyl sulphate, or any other surfactant that doesnot cause gelling, and preferably at a concentration is between 0.01 to5% by weight relative to TiO₂),

[0126] vii) Addition of or mixing with one or more metal precursor(s),

[0127] viii) Addition of or mixing with one or more silane(s)(preferably when added or mixed, and it is a hydrolysable or partiallyhydrolysable silane compound(s) of a formula RSiX₃, R₂SiX₂ and SiX₄(where R is a simple or functionalised organic group and X could be ahalide or an alkoxide group) and preferably added neat or as awater-miscible solution, preferably such that n the silane concentrationis between 1-50%, more preferably 10-35% by total weight.).

[0128] Preferably when one or more metal precursor(s) is added or mixedit is a soluble metal salt or complex one or more of Pd, Pt, Ag and Cu.

[0129] Preferably the metal is one or more of:

[0130] Ag and the precursor is one or more of (but not restricted to)silver acetate or silver nitrate, and/or

[0131] Cu and the precursor is one or more of (but not restricted to)copper acetate, copper sulphate and copper nitrate, and/or

[0132] Pd or Pt and precursor is (but not restricted to) one of thehexachloro-complexes of Pd or Pt.

[0133] Preferably when the metal is Pd or Pt, the Pd or Pthexachloro-complex is mixed with a low carbon organic compound as asacrificial compound, of formaldehyde, formic acid, methanol or ethanol,which added in excess relative to the metal precursor.

[0134] Preferably here is the further step 3) of storing the coatingsolution at any concentration, preferably between 0-20° C., morepreferably between 4-15° C.

[0135] According to an seventh aspect of the invention there is provideda method of preparing a TiO₂-coated substrate comprising or includingthe steps of:

[0136] I. preparation of a coating solution substantially as previouslydescribed, and

[0137] II. further processing of the solution to obtain the coatedsubstrate.

[0138] Preferably the TiO₂ phase in the coated substrate, at leastinitially, includes, is predominantly or is substantially anatase.

[0139] Preferably the substrate is one or more of (but not restrictedto) glass, quartz, glass fibre, woven glass fibre, ceramics, siliconwafers, metals, polymer surfaces (such as polyethylene or polyester),wood, or building materials such as mortar, brick, tiles, or concrete.

[0140] Preferably step II includes

[0141] i) application of the coating solution to a substrate, and

[0142] ii) a gelling step, and

[0143] iii) a curing step.

[0144] Preferably application of the coating solution is effected bytechniques such as (but not restricted to) spin-coating, dip-coating orspraying.

[0145] Preferably prior to application of the coating solution aprotective layer of amorphous silica and/or alumina (and/or precursorsthereof) is applied to the substrate.

[0146] Preferably the precursor(s) for amorphous silica may be selectedfrom (but not limited to) the series tetraalkoxysilanes,alkoxychlorosilanes and the precursors for amorphous alumina may beselected from (but not limited to) the series aluminium trialkoxides,and the precursors are prepared by hydrolysing the silica and/or thealumina precursor(s) in acid solution.

[0147] Preferably curing of the gel is effected by exposure to UVradiation and/or by heat.

[0148] Preferably the wavelength of the UV radiation substantially orpartially coincides with the band gap of anatase TiO₂.

[0149] Preferably the curing time is determined by the amount of oxalicacid to be decomposed and/or the amount of silane (if present) and/orthe amount of surfactant (if present) and/or the wavelength of theradiation and/or the intensity of the radiation.

[0150] Preferably the gelling step is effected by one or more of:

[0151] evaporating the solvent; at room temperature or above;

[0152] evaporating the solvent under a vacuum, with or without heating;

[0153] addition of a gelling agent including (but not restricted to) adilute mineral acid solution such as HCl, HNO₃ or H₂SO₄, or an alkalinesolution such as KOH, ammonia, sodium carbonate or tetraalkylammoniumhydroxide.

[0154] Preferably there is a further step III which includes one or boththe steps of:

[0155] i) impregnation of the titanium containing-product with a metalprecursor, (an impregnation step) and/or

[0156] ii) transformation of any metal precursor added within step I)and/or step III) (a transformation step).

[0157] Preferably the metal of the precursors of step i) is one or moreof Pd, Pt, Cu or Ag, and preferably when the metal precursor is Pd or Ptthe metal precursors is mixed with a sacrificial compound offormaldehyde, formic acid, methanol or ethanol, in excess relative tothe metal precursor.

[0158] Preferably curing of the gel is effected by exposure to UVradiation and/or by heat and/or by evaporation of the solvent, andpreferably a xerogel is produced either as an intermediate, or as aproduct. Preferably, when UV radiation is employed the wavelength of theUV radiation substantially or partially coincides with thephotocatalytically active band gap of the TiO₂ in the anatase phase.

[0159] Preferably the curing time is determined by the amount of oxalicacid to be decomposed and/or the wavelength of the radiation and/or theintensity of the radiation.

[0160] According to an eighth aspect of the invention there is provideda method of preparing a hardened TiO₂-coated substrate comprising orincluding the steps of:

[0161] i) preparation of a coating solution substantially as describedpreviously and wherein at least both an acid and an alcohol are added tothe solution in a certain quantity,

[0162] ii) application of the coating solution to a substrate,

[0163] iii) heating to around 150° C.,

[0164] iv) further heating to around 450° C. to decompose the organicmaterials and/or to effect sintering of the coating.

[0165] According to a ninth aspect of the invention there is provided amethod of preparing a patterned TiO₂-coated substrate comprising orincluding the steps of:

[0166] i) preparation of a coated substrate substantially as describedpreviously prior to any gelling or curing steps (if any),

[0167] ii) masking one or more regions of the coating,

[0168] iii) curing of the unmasked region(s) of coating by exposing theunmarked region(s) to an ultraviolet light to photocatalytically destroythe oxalic acid and other organic materials present in the titaniumoxide of the unmasked region(s),

[0169] iv) development of the film.

[0170] Preferably the coating solution produces a film which contains 50to 100% by weight titania after curing.

[0171] Preferably only one layer of coating solution is applied toobtain sharper and clearer patterns.

[0172] Preferably development of the film is by one or more of:

[0173] i) application of an acid solution wherein the acid solution isany dilute mineral acid such as sulphuric and/or an organic acidsolution such as oxalic, lactic, citric, tartaric or sulphuric acidand/or an acidic salt solution where the salt is, ammonium sulphate oraluminium sulphate and/or;

[0174] ii) application of other materials such as hydrogen peroxideand/or;

[0175] iii) a radicational or mechanical method includingultrasonication, and/or

[0176] iv) any other method for redissolution of the UV—unexposed gel.

[0177] Preferably the development occurs at room temperature, or underconditions of heating, and preferably is followed by a final step ofsintering the coating.

[0178] Preferably there may be one or more additional prior step tosintering including one or both of the steps of

[0179] evaporating the solvent; at room temperature or above and/or

[0180] evaporating the solvent under a vacuum, with or without heating.

[0181] Preferably curing of the gel is effected by exposure to UVradiation and/or by heat, and preferably a xerogel may be produced as anintermediate.

[0182] Preferably when UV radiation is employed the wavelength of the UVradiation substantially or partially coincides with the photocatalytically active band gap of the TiO₂ in the anatase phase.

[0183] According to a tenth aspect of the invention there is provided amethod of increasing the content of rutile and/or TiO₂—B phases in aTiO₂ product including or comprising:

[0184] preparing a TiO₂-containing product as substantially aspreviously described wherein the TiO₂ phase is predominantly or at leastpartially anatase or is predominantly or at least partially TiO₂—Bphase, and

[0185] heating to increase the TiO₂—B and/or rutile content.

[0186] Preferably heating to substantially between 200° C. to 400°causes or initiates phase change of TiO₂—B to anatase phase to titaniumdioxide-B and/or rutile phase in the product. Additionally furtherheating to substantially above 400° C. will increase the content of therutile phase in the product.

[0187] Preferably the TiO₂ undergoes a phase change substantiallyentirely to rutile at temperatures substantially higher than 500° C.

[0188] Alternatively addition of substantially up to 50% by weightsilica results in stabilisation of the anatase and/or TiO₂—B phasethereby requiring heating to over 600° C. to initiate and/or completethe transformation to rutile phase.

[0189] According to an eleventh aspect of the invention there isprovided a TiO₂-containing product substantially prepared according tothe method previously described.

[0190] According to a twelfth aspect of the invention there is provideda TiO₂-containing product prepared substantially as herein describedwith reference to any one or more of the accompanying examples.

[0191] According to a thirteenth aspect of the invention there isprovided a TiO₂-containing coating solution substantially preparedaccording to the method as previously described.

[0192] According to a fourteenth aspect of the invention there isprovided a TiO₂-containing coating solution prepared substantially asherein described with reference to any one or more of the accompanyingexamples.

[0193] According to a fifteenth aspect of the invention there isprovided a TiO₂-containing coated substrate substantially preparedaccording to the method as previously described.

[0194] According to a sixteenth aspect of the invention there isprovided a TiO₂-containing coated substrate prepared substantially asherein described with reference to any one or more of the accompanyingexamples.

[0195] According to a seventeenth aspect of the invention there isprovided a TiO₂-containing hardened film substantially preparedaccording to the method as previously described.

[0196] According to an eighteenth aspect of the invention there isprovided a TiO₂-containing hardened film prepared substantially asherein described with reference to any one or more of the accompanyingexamples.

[0197] According to a ninetheenth aspect of the invention there isprovided a TiO₂-containing patterned film substantially preparedaccording to the method as previously described.

[0198] According to a twentieth aspect of the invention there isprovided a TiO₂-containing patterned film prepared substantially asherein described with reference to any one or more of the accompanyingexamples.

[0199] According to a twenty first aspect of the invention there isprovided a method of preparing a TiO₂-based photocatalyst including orcomprising the following steps:

[0200] 1) preparation of a solution containing colloidal particles whichcontain titanium ions wherein the particles are stabilised by oxalicacid, or stabilised by reaction with oxalic acid,

[0201] 2) further processing of the solution to obtain thephotocatalyst.

[0202] Preferably the TiO₂-based photocatalyst is a TiO₂ particulatematerial, and the further processing includes a gelling and a curingstep.

[0203] Preferably the TiO₂-based photocatalyst is a TiO₂ coating or filmon a substrate, and the further processing includes preparation of acoating solution and application of the coating solution to thesubstrate, and a gelling and a curing step.

[0204] Preferably the TiO₂ phase in the particulate material, coating orfilm, at least initially, includes, is predominantly or is substantiallyanatase.

[0205] Preferably the TiO₂-based photocatalyst acts as a photocatalystupon irradiation of or exposure to UV light.

[0206] Preferably the TiO₂-based photocatalyst is metal or metal-oxidedoped, preferably the metal is selected from Pt, Pd, Cu or Ag.

[0207] Preferably the TiO₂-based photocatalyst can be used tophotocatalytically degrade organic compounds and wherein the degradationoccurs via application of or exposure to UV radiation, and/or theTiO₂-based photocatalyst can act as a hydrophilic surface when coated ona substrate.

[0208] According to a twenty second aspect of the invention there isprovided a TiO₂-based photocatalyst prepared substantially according tothe method as previously described.

[0209] According to a twenty third aspect of the invention there isprovided a TiO₂-based photocatalyst prepared substantially as hereindescribed with reference to any one or more of the examples.

[0210] According to a twenty fourth aspect of the invention there isprovided a method of preparing B phase TiO₂, including or comprising thefollowing steps:

[0211] 1) preparation of a solution containing colloidal particles whichcontain crystalline titanium dioxide wherein the particles arestabilised by oxalic acid, or stabilised by reaction with oxalic acid,and

[0212] 2) further processing of the solution to obtain TiO₂predominantly or substantially in the TiO₂—B phase, and

[0213] 3) heating of the TiO₂ to substantially between 200-300° C.

[0214] Preferably the further processing step 2) includes removal of thesolvent and/or a gelling step and/or a curing step.

[0215] Preferably step 1) is substantially according to one or more ofthe methods described previously in the first-fourth aspects of theinvention.

[0216] Preferably there is a further step 4) of heating beyond 450° C.provide TiO₂ in the rutile phase.

[0217] According to a twenty fifth aspect of the invention there isprovided B phase TiO₂, prepared substantially according to the methodpreviously described.

[0218] According to a twenty sixth aspect of the invention there isprovided B phase TiO₂, prepared substantially as herein described withreference to any one or more of the examples.

[0219] Although the present invention is broadly as defined above, it isnot limited thereto and also includes embodiments of which the followingdescription provides examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0220] In particular, a better understanding of the invention will begained with reference to the accompanying drawings and figures in which:

[0221]FIG. 1 shows a thermal analysis (TGA and DTA) of the powderprepared from gelling the sol in Example 5;

[0222]FIG. 2 shows X-ray diffraction (XRD) patterns of the powderprepared from gelling the sol in Example 9 with no silica added;

[0223]FIG. 3 shows the infrared spectra of the film prepared as inExample 10 and cured by UV light;

[0224]FIG. 4 shows the effect of added SiO₂ on the photoactivity andsurface area using a 2M sol of the invention;

[0225]FIG. 5 shows the change in photoactivity with a catalyst loadingusing 2M sol of the invention +50% SiO₂ coated on woven glass fibre;

[0226]FIG. 6 shows the effect of humidity on the photoactivity using twocoatings of 2M sol of the invention +50% SiO₂ coated on woven glassfibre;

[0227]FIG. 7 shows the UV degradation of some surfactants on TiO2 filmsfollowed by I.R spectroscopy;

[0228]FIG. 8 shows the x-ray diffraction spectrum of TiO2-B containingmaterial;

[0229]FIG. 9 shows the surface profile of a TiO₂ patterned film;

[0230]FIG. 10 shows the scanning electron micrograph (SEM) of a TiO₂patterned film;

[0231]FIG. 11 shows the photodecomposition of Rhodamine B dye on TiO₂film;

[0232]FIG. 12 shows the photodecomposition of ethylene gas on platinisedTiO₂ photocatalyst cloth;

[0233]FIG. 13 shows the photothermal decomposition of ethylene gas on aplatinised TiO₂ photocatalyst cloth; and

[0234]FIG. 14 shows the photothermal decomposition of toluene gas on aplatinised TiO₂ photocatalyst cloth.

DESCRIPTION OF THE INVENTION

[0235] As defined above, the invention relates to processes of preparingsolutions containing colloidal particles which contain titanium (ietitanium-containing sols), and to processes for preparing titaniumdioxide containing materials. In particular xerogels (a gel in which thesolvent has been removed by evaporation at an ambient temperature),powders and coated films can be prepared from the solutions. Further,the invention also relates to the application of the titanium dioxidecontaining materials.

[0236] A. Preparation of Titanium-Containing Materials

[0237] A1—General

[0238] The applicants have found that titanium-containing colloidalsolutions stabilised by oxalic acid can be prepared by stablisation orpeptization. Peptization is the process by which colloidal sols arestabilised usually by addition of electrolytes. In the case of TiO₂ a pHof approximately <4 is required, thus acidic conditions are generallyemployed. These colloidal solutions have certain advantageous propertiesthat render them highly suitable for use in preparing titaniumdioxide-containing materials.

[0239] In particular, the applicants have found that titaniumdioxide-containing materials prepared from such colloidal solutions donot require firing at high temperatures in order to have properties thatmake them suitable for use in such application as photocatalysts. Thisis because titanium dioxide prepared by removal of the solvent from suchcolloidal solutions has been found to contain or to comprise titaniumdioxide directly in the anatase crystalline form. This form is primarilyrequired for titanium dioxide to have photocatalytic properties in theUV range, or is at least the most convenient photocatalytic form oftitanium dioxide.

[0240] Typically, conversion of titanium dioxide from the amorphousform, which is the typical phase produced initially in other processes,to the anatase crystalline form has generally required heating totemperatures of at least 300° C. to 400° C. In contrast, titaniumdioxide materials prepared from the colloidal solutions of the presentinvention can be cured simply by exposure to solar light or anultraviolet light source. Importantly, irradiation of the materials iseffective to remove the oxalic acid present, as the titanium dioxide,which is already in the anatase form, photocatalyses decomposition ofthe oxalic acid.

[0241] The ability of the titanium dioxide materials to be cured withoutthe need for high temperatures enables the preparation of compositematerials comprising a substrate coated with a titanium dioxide film inwhich the substrate used does not need to be heat resistant. Thus,composite materials in which the substrate is, for example, athermoplastic material or wood, can be prepared.

[0242] Alternatively, the titanium-dioxide containing materials of theinvention can be cured by heating to appropriate temperatures.Generally, a temperature of as low as about 200° C. will be sufficientto decompose the oxalic acid present in the material and yield a productin which the titanium dioxide is in the anatase form. Further, anatase,TiO₂—B, rutile phase or a mixture can be obtained, depending on theamount of oxalic acid used in the preparation and on the firingtemperature. Thus, if crystalline TiO₂ as the anatase phase or a mixtureof anatase and titanium dioxide B is desired, the titanium dioxidematerial would generally be cured at a temperature of from about 200° C.to 400° C. Above 400° C. a mixture of anatase and rutile will generallybe obtained, which will transform completely to rutile at hightemperatures, as is known in the art.

[0243] The production of the titanium dioxide materials is carried outin two stages—firstly preparation of titanium containing colloidalsolutions or sols, and then the preparation of the titanium-containingmaterials.

[0244] A2. Production of Titanium Sols

[0245] The solutions containing colloidal particles containingcrystalline titanium dioxide of the present invention (the titaniumsols) may be prepared by reacting a mixture containing a hydrolysabletitanium-containing compound and oxalic acid, in a reaction medium whichcomprises either water or a mixture of water and an alcohol.

[0246] The titanium-containing compound used may be atitanium-containing compound that is hydrolysable in water or base.Also, the use of mixtures of two or more hydrolysabletitanium-containing compounds is within the scope of the presentinvention.

[0247] It is particularly preferred that the water hydrolysabletitanium-containing compound is a compound of the formula Ti(OR)₄, whereR is a C₂-C₆ linear or branched chain alkyl group. Two preferredtitanium-containing compounds are titanium tetraisopropoxide andtitanium tetrabutoxide, which are hydrolysable in water.

[0248] Alternative titanium-containing compounds that may be usedinclude TiCl₄ and TiOSO₄, which can be hydrolysed using a base prior toreaction with oxalic acid. In this case the hydrolysed products(hydrated titania or titanic acid) would preferably be filtered andwashed, preferably with deionised water, before reaction with the oxalicacid. The hydrolysed product is more preferably used as slurry withoutdrying.

[0249] The hydrolysable titanium containing compound may, for example inthe case where the compound is of the formula Ti(OR)₄, be first combinedwith a solution of oxalic acid in alcohol followed by addition of water.Alternatively, the titanium-containing compound may just be addeddirectly to water (or to a mixture of water and an alcohol), then oxalicacid is added to the so formed slurry. Otherwise the titanium-containingcompound may be added to a solution of oxalic acid in water or inwater/alcohol solution.

[0250] The oxalic acid may be either anhydrous oxalic acid, or hydratedoxalic acid, such as H₂C₂O₄. 2H₂O. It is preferred that the amount ofoxalic acid is such as to provide a mole ratio of oxalic acid:titaniumin the range of about 0.2:1 to about 1:1 to get the sols. Below 0.2ratio either very white colloids or unstable colloids are obtained.

[0251] As indicated above, the reaction medium can comprise either wateror a mixture of water and an alcohol. It is preferred that the watercontent is such as to provide a mole ratio of water:titanium in therange of from about 200:1 to about 800:1, more preferably from about400:1 to about 600:1. Below 200:1 ratio peptization becomes difficultand may produce unstable colloids. The preferred amount of alcoholpresent is such as to provide a mole ratio of alcohol:titanium of fromzero to 100:1, more preferably 10:1 to 50:1.

[0252] It is preferred that the alcohol, when present, is a monohydroxyl aliphatic alcohol having the formula ROH, where R is a C₁ to C₄linear or branched alkyl group, such as ethanol or t-butanol.

[0253] In order to form a sol, ie a solution containing colloidalparticles containing titanium ions, the reaction mixture is preferablystirred or agitated, at a temperature between ambient temperature tonear the boiling point of the mixture, more preferably at a temperaturebetween about 40° C. and about 80° C.

[0254] The sol can be stored at any desired concentration level,preferably up to about 32% by weight TiO₂. It is however preferred thatif a concentrated sol is prepared, that this be then diluted with waterto give a concentration of about 2-20% by weight as TiO₂ for preparationof thin films.

[0255] The reaction time required to form a colloidal solution willdepend on the composition and concentration of the reaction mixture.However, in general, the required reaction time will range from about 15minutes up to about 3 hours.

[0256] The sols thus prepared will contain colloidal particles of asubmicrometer to a few nanometer sizes, or less and containing titaniumions, with the particles being stabilised by oxalic acid.

[0257] Without wishing to be bound by any theory, it is thought that thestructure of the colloidal particles is likely to be nTiO₂.H₂C₂O₄ orsimilar, where n is a number greater than or equal to 1, ie TiO₂particles stabilised by oxalic acid or any of its dissociated forms, andthat the oxalic acid prevents the titanium dioxide precipitating out ofthe solution.

[0258] A3—Preparation of the Titanium Dioxide Solid Materials

[0259] Once prepared, the sols may be irradiated by UV light to reducethe concentration of oxalic acid in the sol, especially when the oxalateconcentration is about 0.5 mole ratio or higher relative to Ti. The UVlight may conveniently be provided by a mercury lamp or a xenon lamp orany other intense UV source with a wavelength less than 400 nm.

[0260] The titanium-containing colloidal solutions may, by removal ofthe solvent, be used to prepare titanium dioxide or titaniumdioxide-containing materials, including titanium dioxide powders andcomposite materials comprising a substrate coated with a film oftitanium dioxide.

[0261] In one embodiment of this invention, if a titanium dioxide powderor film of higher surface area is to be prepared, it is usuallypreferred that the sol is first mixed with colloidal silica, in anamount of between about 1 and 99 weight percent relative to titanium,preferably from 30 to 60 wt % relative to titanium. The concentration ofcolloidal silica used can have any desired concentration, but ispreferably between about 1 and 50% by weight.

[0262] A further option within the invention is to use a titania solprepared according to the above, and further mix it with a hydrolysableor partially hydrolysable silane compound of a formula RSiX₃ and SiX₄(where R is a simple or functionalised organic group and X could be ahalide or an alkoxide groups that may exist together) before causing thesol to gel. Such a silane can be added as neat or as solution in anaqueous or organic solvent that is miscible with water, such as ethanol,acetone, etc. Such a silane material can form a linkage between titaniaparticles through —Ti—O—Si—O—Ti— bonding. This can suppress crystalgrowth of the titania particles as well as add better abrasionproperties to the photocatalyst.

[0263] To prepare a xerogel or a powder, the sol is then preferablycaused to gel. This may be achieved by evaporating the solvent at roomtemperature or above, or under a vacuum with or without heating.Alternatively, the sols can be caused to gel by adding a dilute mineralacid solution, such as HCl, HNO₃ or H₂SO₄, or an alkaline solution, suchas KOH, ammonia, sodium carbonate or tetraalkylammonium hydroxide. Thesegels can if desired be redissolved in acidic solutions, such assulphuric, nitric, oxalic, citric, lactic and tartaric acids, etc. atroom temperature or by heating, depending on the type and concentrationof the acid. The process of redissolving the gelled material isparticularly important in film patterning, as it will be describedlater.

[0264] The gels can be cured to remove the oxalic acid and form titaniumdioxide containing materials or films, by exposure to solar light or aUV light source, or by heating at appropriate temperatures. If a UVsource is used, this can be a mercury lamp, a xenon lamp, a black lightlamp, or other UV source. The wavelength of the light can be below 400nm to coincide with the band gap of the titania photocatalyst. Therequired curing time will depend on the film thickness, the amount ofoxalic acid to be decomposed, the wavelength of the radiation and itsintensity. The UV cured material will contain TiO₂ in the anatase form.The curing process of a film prepared as in Example 10 below wasmonitored by infrared spectroscopy (FIG. 3).

[0265] Alternatively, the gels can be cured by heating at appropriatetemperatures as will be known in the art, to form anatase, TiO₂—B orrutile. At temperatures as low as 200° C. to 400° C., crystalline TiO₂,as the anatase phase or a mixture of anatase and titanium dioxide-B, isobtained. Above 400° C. a mixture of anatase and rutile will beobtained, which will transform completely to rutile at high temperature.This was monitored using thermal analysis (TGA, DTA) (FIG. 1) and powderX-ray diffraction (XRD) (FIG. 2). In this case the crystallite sizegradually increased from 37 Å in the xerogel to 58 Å after heating at300° C. for 1 hour, then rapidly increased above 100 Å accompanied withthe formation of rutile. When silica (Nalcogel colloidal silica) waspresent with the titanium dioxide, the anatase form could be stabilisedat higher temperature with a small change in the anatase crystallitesize. As one can see from the examples given below, if the materialcontains 50% by weight silica the anatase phase can be stabilised up to600° C. and the anatase crystallite size will change from 37 Å in thexerogel to only 56 Å after heating at 600° C. for 1 hour. Thereforeinclusion of silica into the photocatalyst can stabilise the anatasephase and increase the surface area of the material, thus improves itsphotocatalytic activity (FIG. 4). The highest surface area andphotoactivity obtained was with the 50% by weight SiO2 for which thespecific surface area was 246.3 m²/g according to BET method fornitrogen sorption. The pore size distribution according to BJH analysisof the nitrogen desorption isotherm showed a maximum at 35 Å porediameter and cumulative pore volume of pores between 17 and 100 Å of0.1125 cm³/g with the average pore diameter of 28.2 Å. However, for thepure titania powder the surface area was 153 m²/g according to BETmethod. The pore size distribution according to BJH analysis showed asmaller maximum at 34.3 Å pore diameter and cumulative pore volume ofpores between 17 and 100 Å of 0.02254 cm³/g with the average porediameter of 24.5 Å. It is clear that blending amorphous silica canchange the surface properties and increase the surface area of thematerial described in this invention, which is important for adsorptionof pollutants.

[0266] Film Production

[0267] In order to prepare titanium dioxide films, thetitanium-containing colloidal solutions may initially be mixed with oneor more compounds that enhance the film-casting process to producethicker and more abrasion resistant films. Water soluble alcohol, asmuch as 50%, has been found to enhance the film-forming process. Inparticular methanol and ethanol gave better results in spray coating.The sols may also be mixed with any proportion of water-soluble oralcohol-soluble ketones, such as acetone and acetylacetone.

[0268] Further, the sols may be mixed with any proportion of organicacids. The organic acid can be mono-, di- or multi-functional and it mayalso contain hydroxyl groups. Such acids include for example acetic,lactic, tartaric, citric, maleic, malic, malonic, diglycolic, benzoic,1,2,4,5-C₆H₂ (COOH)₄, EDTA, and mixtures thereof.

[0269] The sols may also be mixed with any proportion of water-solublealiphatic or aromatic alcohols, diols or polyols. Examples of suchcompounds include ethanol, propanol, ethylene glycol, glycerol,polyethylene glycol, polyvinylalcohol, phenol, catechol, polysaccharidesand other polyols as will be known by persons skilled in the art, or amixture of the same.

[0270] The sols may also be mixed with any proportion of ethanolamines,such as monoethanolamine, diethanolamine and triethanolamine, or amixture thereof.

[0271] When such acids and alcohols are added together to the sol in acertain quantity, the sol can be coated on a substrate and heated toaround 150° C. to give a polymeric hard film which allows the coatedsubstrate to be easily handled. This characteristic has manyapplications, especially for example, in the robotic industry. This canbe heated further to decompose the organic material and produce theanatase coating.

[0272] The applicants also prefer blending of amorphous silica byaddition of silica colloid and/or silane compounds as mentioned earlierto the titanium dioxide colloid prepared in this invention. Such silanecompounds may act as particle couplers to help improving the filmthickness and getting more abrasion resistant films, which then eitherbe cured under UV irradiation or heating to decompose any organicresidues.

[0273] In addition, and especially if the film is to be formed on ahydrophobic surface such as some polymer surfaces, the sols may be mixedwith any proportion of surfactant. The surfactant can be chosen from butnot limited to the Brij series, Triton series, Tergitol series, Pluronicseries, potassium dodecyl sulphate, or any other surfactant that doesnot cause gelling. Preferably, the surfactant concentration is between0.01 to 5% by weight relative to TiO₂.

[0274] Coated Substrates

[0275] The sols thus prepared can be coated on a variety of substrates.Examples of such substrates include glass, quartz, glass fibre, wovenglass fibre, ceramics, silicon wafers, metals, polymer surfaces (such aspolyethylene or polyester), wood, or building materials such as mortar,brick, tiles, or concrete. The coating method used may be any suitablemethod known in the art, such as spin-coating, dip-coating or spraying.

[0276] It is also preferred to apply a protective layer of amorphoussilica or alumina on the substrate before coating with thephotocatalyst, especially if the substrate consists of organic materialssuch as a polymer that could be deteriorated by the photocatalystcoating. The same method can be done with glass and other supportedfilms that are prepared by heating. The precursors for amorphous silicaand alumina can be prepared by hydrolysing a silicon alkoxide or analuminium alkoxide in acidic solutions as is known to those who areskilled in the art. For examples precursors for amorphous silica andalumina can be chosen from the series tetraalkoxysilanes,alkoxychlorosilanes and aluminium trialkoxides but are not limited tothese. It is more preferred that the alkoxy radicals would have lowcarbon backbones of C1-C5.

[0277] The films that are coated with the photocatalyst can be cured asdescribed above, ie by exposure to solar light or a UV light source, orby heating at appropriate temperatures.

[0278] Fine Patterned Films

[0279] In the present invention, the applicants have been able toproduce fine line patterns of less than 4 micrometer wide with verysharp edges using a low intensity black light lamp. This will enable theformation of TiO₂ patterns on polymeric substrates.

[0280] In one form of this invention it is possible, by utilising thephotocatalytic properties of the titanium dioxide containing material asprepared by the present method, to produce a substrate coated with filmshaving different patterns.

[0281] The coating solution may be chosen from any combination of thetitania colloid with a silica colloid, a hydrolysable or partiallyhydrolysable silane and a surfactant. However it is preferred that thecoating solution will produce a film which contains 50 to 100% by weighttitania after curing. The titania content of the coating solution willbe chosen so that it produces the required thickness of the patternedfilm. It is also preferred to apply only one layer to get sharper andclearer patterns. The patterning process comprises two steps. In thefirst step, parts of the film may be masked and the unmasked parts areexposed to an ultraviolet light. This will photocatalytically destroythe oxalic acid and other organic materials present in the titaniumoxide of the unmasked portions.

[0282] The next step is to develop the film by acid treatment. Thedestruction of the oxalic acid in the unmasked parts renders those partsof the film insoluble, whereas the parts of the film that have not beenexposed to UV light can be dissolved using a suitable acid solution orany material that reacts with or dissolves oxalic acid and or thetitanium dioxide-containing gel, since such parts of the film are notcured. The acid solution may be any dilute mineral acid, organic acidsolution or an acidic salt solution. Preferably, the acid is oxalic,lactic, citric, tartaric or sulphuric acid. The acidic salt can be, forexample, ammonium sulphate or aluminium sulphate. Other materials suchas hydrogen peroxide may also be used to develop the patterns.Additionally or alternatively a radiational or mechanical method such asultrasonication can be used to develop the patterned film by removingthe uncured parts.

[0283] In this way titanium dioxide films having very fine patterns offew micrometers wide or less and submicrometer to few nanometer thickcan be produced on a variety of substrates, including plastic andpolymeric surfaces, since it is done at room temperature and low levelUV light (FIGS. 9, 10). This process may find a particular industrialapplicability in the electronics industry such as field-effecttransistors and other microdevices.

[0284] Doping

[0285] Here we describe at least two methods of dispersing platinum andother metal particles by photo- and chemical reduction in TiO₂ films andpowders that are prepared in this invention.

[0286] The properties of the titanium dioxide-containing powders andfilms, for example the photocatalytic properties, may be enhanced bydoping with a metal salt or complex. Suitable dopants will be known tothose persons skilled in the art.

[0287] The composite may be either heated at a suitable temperature toform the metal oxide or UV irradiated to form metal particles inside thetitanium dioxide or some cases can produce metal oxides. The addition ofa soluble metal salt or complex may either be directly to the sols or byimpregnation of the powders and films themselves with an aqueous oralcoholic solution of the metal salt for a sufficient time to allowadsorption. When the metal is chosen from the group Pd, Pt, Ag and Cu,the adsorbed metal salt or complex can be either thermally decomposed orphotocatalytically decomposed under UV light. The photocatalytic dopingprocess may take between few minutes to several hours. Thephotocatalytic process will involve photooxidation of the organicradical of the metal precursor and the photoreduction of the metal ionto zero oxidation state whereby the metal particles are disperseduniformly on the surface of the catalyst particles. The final metalcontent in the photocatalyst is preferably less than 2% by weight andmore preferably between 0.2 to 0.5% by weight. Above 0.5% by weightdoping the activity of the photocatalyst may marginally increase.

[0288] In this method the preferred precursor for Pd and Pt are thehexachloro-complexes. It is preferred to mix these precursors with asacrificial compound, more preferably the sacrificial compound is a lowcarbon organic compound such as formaldehyde, formic acid, methanol orethanol that is added in excess relative to the doping metal. Forexample, if platinum and formaldehyde are to be used, the morepreferable molar ratio is about 1:5 of Pt:formaldehyde.

[0289] For silver deposition the applicants prefer to use either silveracetate or silver nitrate, although other soluble silver compounds canbe used. The precursor solutions can be added either to the colloid orimpregnated in the catalyst particles or films after curing. Nosacrificial agent is needed in this case. The colour of the silveredcatalyst ranges between light grey to black.

[0290] In this invention the preferred copper precursors are copperacetate and copper nitrate, although other salts such as the sulphatecan be used. The copper precursor can be added to the colloid beforegelling or impregnated in the photocatalyst particles or films aftergelling and curing. The colour of the catalyst will change from lightgreen to bronze due to the reduction of Cu(II) to Cu(0) after exposureto UV light.

[0291] In another embodiment reduction of the metal precursor that isadsorbed on the titanium-containing catalyst can be performed byexposing such a catalyst to a dilute hydrazine hydrate solution for asufficient time to allow the complete reduction of the metal to zerovalency. In this case it is preferred to wash the catalyst with water toremove the excess of hydrazine. In this method hydrazine can penetrateinto the catalyst particles or grains and reduce the metal precursorthat is adsorbed inside the grains, whether the particles are of puretitania, a titanium-containing material, or silica particles.

[0292] B. Application of Titanium Dioxide Materials

[0293] The titanium dioxide powders, grains and composite materialscontaining titanium dioxide materials have a number of applications.

[0294] For example, the materials will perform as photocatalysts. Thematerial is able to decompose organic compounds or pollutants in air andwater under solar radiation or UV light. In particular the undesirablycarbon structures are broken down into relatively harmless CO₂ and H₂O.Dyes can be photocatalytically discoloured or bleached using thematerials prepared in this invention when irradiated with sunlight orartificial UV light. In this invention we present for example, a methodfor preparing and supporting a photocatalyst that is capable of reducingethylene concentration rapidly and efficiently.

[0295] A particular example includes the filtering of ethylene (ethene)gases from horticultural storage facilities. This is a colourless gasproduced by some fruits as they ripen. However, this gas also causespremature ripening of other fruits stored in the same facility. Anexample is the storage of apples and kiwifruit, where the formerproduces ethene that prematurely ripens the latter. This is asignificant issue for horticultural exporters, as it may damage theirproduct before it reaches the market.

[0296] In addition, the titanium dioxide films will havesuperhydrophilic properties when they are first prepared. Thishydrophilicity is maintained by exposure to solar light or UV light,with a contact angle close to zero. This hydrophilicity is particularlyuseful for such applications as anti-fogging mirrors and glass windows,where the hydrophilic surface will prevent the formation of small waterdroplets, that cause the fogging.

[0297] Furthermore, the titanium dioxide-containing materials haveanti-microbial activity, including activity against bacteria, virusesand fungi. These properties may be utilised for example in forming asurface such as a bench top, or tiles coated with a film of titaniumdioxide, to reduce or eliminate the growth of micro-organisms.

[0298] The advantages of the applicant's invention include thefollowing:

[0299] the ability to coat a wide range of surfaces including plasticsand other thermally unstable substances

[0300] curing within 30 minutes under sunlight and les under UV lightsource

[0301] reduced costs related to equipment, energy savings and plantoperation

[0302] ability to produce an abrasion-resistant finish at highertemperatures

[0303] ability to produce large sample sizes easily

[0304] coatings have high porosity and surface area ensuring highphotocatalytic activity

[0305] although high temperatures are needed to ensure that the materialor coating produced is abrasion resistant, relatively low temperaturescan be used where abrasion resistance is not an issue—for example in anair filter where the material does not come into physical contact withanything other than air or gases

[0306] extensive testing has demonstrated that the TiO₂ material ishighly effective at breaking up ethylene and other workplace compounds.Decomposition of these materials has improved from 30% to 95% per hour,illustrating the effectiveness of this invention as a scrubber.

[0307] The invention will now be described in more detail with referenceto the following non-limiting examples.

C EXAMPLES Example 1

[0308] Preparation of Titania Sol Using Titanium Tetraisopropoxide(TTIP) and UV Light

[0309] 14.2 g of TTIP was added to 3.15 g of oxalic acid dihydratesolution in 20 ml absolute ethanol. The mixture was stirred for 10minutes then solvent was evaporated under vacuum. Water was added to thewhite solid and the mixture was stirred at 75° C. to peptize it into aclear sol. The solution then was irradiated by a UV light using amercury lamp for 3 hours. During that the amount of oxalic acid droppedto half its original concentration as determined by permanganatetitration.

Example 2

[0310] Preparation of Titania Sol Using in situ α-Titanic Acid and 0.5Mole Ratio of Oxalic Acid

[0311] α-Titanic acid was obtained by hydrolysing 14.2 g TTIP in 100 mlwater. 3.15 g of oxalic acid dihydrate was added and the mixture wasstirred at 70° C. to form a colourless sol.

Example 3

[0312] Preparation of Titania Sol Using α-Titanic Acid Prepared fromTTIP and 0.5 Mole Ratio of Oxalic Acid

[0313] 14.2 g of TTIP was added to oxalic acid solution in water (150ml). The mixture was stirred at 70° C. to form the sol as described inExample 2.

Example 4

[0314] Preparation of Titania Sol Using α-Titanic Acid from TitanylSulfate

[0315] Titanyl sulphate solution was hydrolysed with dilute ammoniasolution to get a white precipitate, which was filtered and washed withdistilled water until it became free of sulphate. The resulting slurrywas kept in a closed container and analysed for the content of TiO₂ byheating a specimen in a furnace to 500° C. 21 g of α-Titanic acid slurry(19% by weight TiO₂) was added to 200 ml of water containing 3.15 g ofoxalic acid dihydrate. The mixture was stirred at 70° C. to form abluish-white colloid after 1 hour. Powder XRD measurement after gellingand heating to 200° C. showed the presence of anatase phase. Anatasediffraction lines became sharper after heating to 300° C. for 30minutes.

Example 5

[0316] Preparation of Titania Sol Using α-Titanic Acid and 0.3 MoleRatio of Oxalic Acid

[0317] 1.42 g of TTIP was hydrolysed in 40 ml water to form α-titanicacid. 0.19 g of oxalic acid solution in water was added and the mixturewas stirred at 65-70° C. to get a colloidal solution. Powder XRD showedthe presence of anatase phase.

Example 6

[0318] Preparation of Titania Sol Using α-Titanic Acid and 0.25 MoleRatio of Oxalic Acid

[0319] 14.2 g of TTIP was added to oxalic acid (1.57 g) solution inwater (400 ml). The mixture was stirred at 65° C. to get a bluish-whitecolloid. Anatase phase was detected in the xerogel prepared once thesolvent was removed.

Example 7

[0320] Preparation of Titania Sol Using Titanium Tetraisopropoxide(TTIP) and 0.5 Mole Ratio of Oxalic Acid.

[0321] 14.2 g of TTIP was added to 3.15 g oxalic acid dihydrate solutionin 50 ml absolute ethanol. The so formed complex was hydrolysed with 200ml water and the mixture was stirred at 58° C. until a clear sol wasobtained.

[0322] Powder XRD after gelling and heating the powder to 200° C. showedthe presence of a relative 74% TiO₂—B phase and 26% anatase phase. Thepowder heated to 250° C. showed that some of TiO₂—B was transferred toanatase with ratios of 57% TiO₂—B and 43% anatase. Between 300° C. to410° C. only well crystalline anatase was obtained. Transfer to rutilephase started to occur after heating at 450° C. (FIG. 8).

Example 8

[0323] Preparation of Titania Sol Using Titaniumtetrabutoxide (TTB) and0.25 Mole Ratio of Oxalic Acid.

[0324] 17 g of TTB was added to 1.57 g oxalic acid solution in 40 mlt-butanol. The complex was hydrolysed with 500 ml of water and themixture was stirred at 65° C. to get a clear sol. The sol was gelledthen heated to 350° C. to get an off-white anatase powder.

Example 9

[0325] Preparation of Titania Sol Containing 30% Silica

[0326] A mixture was prepared as in Example 6. 5.7 g of Nalcogel brand30% Silica colloid was added to the slurry and the resultant mixture washeated at 60° C. until a clear colloid was obtained.

Example 10

[0327] Titania Sol from TTIP

[0328] 14.2 g of TTIP was added to 1.57 g hydrated oxalic acid in 40 mlabsolute ethanol and stirred for five minutes at 50° C. The solution washydrolysed with 400 ml of warm water and the mixture was stirredvigorously at 65° C. for two hours. The volume of the resulting clearsol was reduced to 50 ml under vacuum to get 8% by weight or to 25 ml toform 16% by weight colloid. The colloid was filtered using 0.4micrometer Sartorius Minisart filter.

Example 11

[0329] Preparation of Titanium Sol Containing 50% Silica

[0330] A sol was prepared as in Example 10, then the required amount ofNalcogel brand 30% silica colloid was added.

Example 12

[0331] Low Temperature Preparation of Photocatalyst Grains and Powders

[0332] 16-20% pure titania colloids or titania-silica colloids wereprepared according to the examples above then were caused to gel. Ifgrains are desired it was preferred to gel the colloid at 70-80° C., andif powders were desired it was preferred that the solvent is evaporatedunder vacuum at 50° C. Heating of such grains or powders at 200° C. forone hour produced anatase photocatalysts. The heating time can be madelonger than one hour to increase the crystallite size.

Example 13

[0333] High Temperature Formation of Photocatalyst Grains and Powders

[0334] A 16% titania/silica colloid was prepared as in example 11. Thecolloid would preferably be gelled at 80° C. if grains were desired, butwhen a powder was desired the solvent was evaporated under vacuum first.The xerogels were heated at 500° C. for one hour to get ananocrystalline anatase containing material, with crystallite size of8.1 nm.

Example 14

[0335] Preparation of Thin Film and UV Curing at Room Temperature

[0336] The sol in Example 10 was coated on a 2×1 cm silicon plate. Thefilm was exposed to mercury UV light at a distance of 5 cm for 30minutes. Decomposition of the oxalate was monitored by infra redspectroscopy. (FIG. 3).

Example 15

[0337] Degradation of Surfactants on a TiO₂ Film

[0338] One drop of each of 2% by weight of surfactant solutions (Brij98, Brij 97, Brij 78, Brij 58, Brij 35, Triton X-100, Tergitol 15-S-12)was spread on the film of example 14, each at a time and left to dry atroom temperature. The films were subjected to irradiation from mercuryUV lamp at a distance of 5 cm. The concentration of the surfactants wasmonitored using infrared spectroscopy. The absorption peaks for C—Hstretching at around 2900 cm⁻¹ and for C—O—C bending at around 1100 cm⁻¹were found to disappear after 30 minutes of irradiation in the Brijseries and after 50 minutes for Triton and Tergitol surfactants (FIGS.7a and 7 b). This indicates that the TiO₂ film cured at room temperaturecan photodegrade these surfactants under UV irradiation.

Example 16

[0339] TiO₂ Film on a Polymer Sheet

[0340] 50×50×3-mm polyacrylic sheet was spin coated with TiO₂ using a 4%sol of Example 10 containing 0.2% Brij 97 surfactant. The film wasirradiated under black light lamp for 2 hours. Coating was repeated inthe same way to get a hydrophilic coating.

Example 17

[0341] Preparation of Thin Film and UV Patterning

[0342] The 4% sol in Example 10 containing 0.1% Brij 97 was spin coatedon a 5×5×0.1 cm glass plate. A black and white image printed on atransparent thin cellulose acetate sheet was placed on the film surface.The plate was exposed to a black light lamp for 6 hours. The film wassoaked in a dilute warm lactic acid solution to dissolve the unexposedarea of the film and leaving the parts that were exposed to the UVradiation.

Example 18

[0343] TiO₂/25%SiO₂ Finely Patterned Film

[0344] 10 ml of the 8% titania sol of Example 10 was well mixed with 0.1g of 2% Brij 97 surfactant and 1 g of glycidoxypropyltrimethoxysilane.The mixture was spin coated on a pre-cleaned 50×50×1 mm glass plate. Afinely patterned mask was securely placed on the film and was irradiatedfrom the top at 10 cm distance under a black light lamp for 15 hours.The mask was removed and the film was soaked in a dilute warm lacticacid for 15 minutes. The so formed pattern was traced by a DETAK surfaceprofiler (Sloan Technology Corporation) (FIG. 9) and by SEM (FIG. 10).

Example 19

[0345] A Hydrophilic Photocatalyst Thin Film at Room Temperature

[0346] A spin coating mixture, which contains 55% by weight TiO₂ and 45%by weight SiO₂ was prepared by mixing 12 ml of 8% titania colloid fromExample 10, 1.164 g of 30% Nacogel silica colloid, 1.716 g ofglycidoxypropyl-trimethoxysilane and 0.1 g of 2% Brij 78 solution. Aclean glass plate was spin coated with this mixture at 600 rpm for 2minutes. The so coated plate was irradiated under black light lamp for15 hours, after this the film became hydrophilic. Film thickness was 0.5micrometer and the film did not scratch when tested by H9 pencil.

Example 20

[0347] Preparation of Heat Cured Thin Film and Testing forHydrophilicity

[0348] The sol in Example 5 was spin coated on 50×50×1 mm glass plate.The plate was heated to 200° C. After cooling, the plate was coatedagain and heated. Five coatings were applied in this way. The film wasstained with 0.1% oleic acid solution in acetone and left under the sunlight. Decomposition of the oleic acid was estimated by the reduction ofthe contact angle of water on the surface, which was reduced to itsoriginal angle of <2 after 6 hours.

Example 21

[0349] Preparation of Heat Cured Film on Woven Glass Cloth

[0350] A piece of woven glass cloth (6×6 cm) was dip coated with the solas prepared in Example 11. After drying in warm air, the cloth washeated at 210° C. for 15 minutes. The coating was repeated to producemultiple layers of the anatase catalyst.

Example 22

[0351] Testing the Photoactivity of Coated Glass Cloths (Degradation ofAcetaldehyde)

[0352] A piece of woven glass cloth prepared in Example 21 was placed ina one litre gas tight reactor with a quartz window at the top. Thereactor is provided with a small fan, and a thermohygrometer. Thehumidity was adjusted to 25±1% at 20° C. Acetaldehyde gas was injectedin the reactor to give a concentration between 40-60 ppm. After 30minutes equilibrium in the dark the coated glass cloth was irradiated bya black light lamp at 4 cm distance. The concentration of acetaldehydewas monitored using gas detectors.

[0353] The effect of added silica on the activity is shown in FIG. 4.The decomposition rate of acetaldehyde versus the number of coatings(thickness of the film) is shown in FIG. 5.

Example 23

[0354] The Effect of Humidity on the Photodegradation of Acetaldehyde

[0355] The humidity effect on the photodecomposition of acetaldehyde wasalso tested. The humidity range used for testing was between about 10and about 90% relative humidity at 20° C. The humidity inside thereactor was changed either by circulating the air through a desiccant orby adding water vapour prior to the injection of acetaldehyde. Theeffect of humidity on the photoactivity is shown in FIG. 6.

Example 24

[0356] Photo-Platinised Photocatalyst Glass Cloth

[0357] A 6×6 cm woven glass cloth was prepared as in Example 21, then itwas heated to 500° C. for 1 hour. Three millilitres of a doping solutioncontaining 0.1% by weight platinic acid and 0.5% by weight formaldehydewas sprayed on the surface of the catalyst and allowed 5 minutesequilibrium time. The wet glass cloth was irradiated under UV light froma 20-Watt black light lamp for 5 minutes during which the colour of thecatalyst changed to grey-black. The glass cloth was washed withdistilled water and dried at 80° C. to get a platinised photocatalyst.

Example 25

[0358] Photo-Silvering a Photocatalyst Glass Cloth

[0359] A 25 ml of 16% by weight titania colloid was prepared as inexample 10 and was well mixed with 1.26 ml of 1% silver nitrate solutionproducing a colloid with 0.2% by weight silver relative to TiO₂. A 6×6cm glass cloth was coated with this solution and dried at 70° C., thenheated at 210° C. for 15 minutes. The photocatalyst cloth was irradiatedunder black light lamp for 30 minutes, during which its colour changedto grey.

Example 26

[0360] Silvering a Photocatalyst Glass Cloth Using Hydrazine

[0361] A photocatalyst glass cloth was prepared as in Example 25. Afterheating to 210° C. the cloth was cooled to room temperature then sprayedwith a 1% hydrazine hydrate solution. After 5 minutes the cloth waswashed with distilled water to remove excess hydrazine, then dried inthe oven. Before using this cloth in photocatalysis experiments, it ispreferred to irradiate it under UV light to photo-degrade any traces ofadsorbed hydrazine.

Example 27

[0362] Copper Doped Titania Thin Film

[0363] 20 ml of 4% titania containing colloid from Example 10 was mixedwith 0.5 ml of 1% copper acetate solution to give 0.2% by weight Curelative to TiO₂. After addition of 0.1% Brij surfactant the solutionwas spin coated on a clean glass plate. The coated plate was irradiatedunder black light lamp for 5 hours, then another layer was applied bythe same way. This film can be used as antibacterial coating.

Example 28

[0364] Photodegradation of a Dye

[0365] The film that was prepared as in Example 20 by heating to 200° C.was stained with 0.5% alcoholic solution of Rhodamine B base. Thestained film was placed on a laboratory bench facing sunlight that wascoming through a window. The fading of the dye colour was monitoredusing a Hewlett Packard diode array UV-visible spectrophotometer atwavelength 540 nm. It took 15 min for the dye on the film to completelydisappear and become hydrophilic again (FIG. 11).

Example 29

[0366] Photodegradation of Ethylene Gas

[0367] A 6×6 cm platinised photocatalyst cloth was prepared as inExample 24 loaded with 0.09 g of the photocatalyst. The photocatalystcloth was placed inside a 150 ml gas tight reactor. The humidity insidethe reactor was adjusted to 40% at 20° C. 1 ml of 1% ethylene gas in airwas injected into the reactor to produce 70 ppmv of ethylene inside thereactor. After 30 minutes equilibrium, the black light lamp was turnedon and the ethylene concentration was monitored using a Hewlett Packard6890 gas chromatograph equipped with an Innowax column and FID detector.After 30 minutes the temperature inside the reactor became 40° C. and97.1% of the ethylene was decomposed (FIG. 12).

Example 30

[0368] Photothermal Degradation of Ethylene Gas

[0369] A 11×17 cm platinised photocatalyst cloth was prepared as inExample 24 which was loaded with 0.6 g photocatalyst. Humidity in thephotoreactor was adjusted to 41% at 20° C. 0.6 ml of pure ethylene gas(26.78 micromole) was injected. After 30 minutes equilibrium, the UVlamp (black light lamp) and heat were turned on with the temperatureinside the photoreactor was raised to 85° C. The concentration ofethylene was monitored by GC as in Example 29 and was found to bereduced by 98.9% after 30 minutes (FIG. 13)

Example 31

[0370] Photothermal Degradation of Toluene

[0371] The same platinised photocatalyst cloth of Example 30 was usedand the humidity inside the reactor was 47% at 20° C. A 2.5 microlitreof pure liquid toluene (20 micromoles) was injected inside the reactorand left to evaporate and adsorbed on the photocatalyst for 40 minutes.The black light lamp and the heat were turned on to raise thetemperature inside the reactor to 85° C. The concentration of toluenegas was monitored using the same technique as in Example 29. After 30minutes the concentration of toluene was reduced by 93.8% and in onehour in was reduced by 99.4% (FIG. 14)

[0372] While the invention has been described with reference toparticular embodiments and examples, those persons skilled in the artwill appreciate that variations and modifications may be made withoutdeparting from the scope of the invention.

1. A method of preparing a solution containing colloidal particles whichcontain titanium ions comprising or including the step of: A. reactingor otherwise stabilising one or more hydrolysable titanium-containingcompound(s) with oxalic acid in a reaction medium.
 2. A method ofpreparing a solution as claimed in claim 1 wherein A occurs underconditions such that peptization of the colloidal solution issubstantially obtained and substantially maintained.
 3. A method ofpreparing a solution as claimed in claim 2 wherein the conditionsinclude stirring or agitation of the one or more hydrolysabletitanium-containing compound(s) with oxalic acid in the reaction medium,at a temperature between ambient temperature to near the boiling pointof the reaction mixture.
 4. A method of preparing a solution as claimedin claim 3 wherein the reaction medium comprises water or awater/alcohol mixture and wherein the titanium-containing compound ishydrolysable in water and/or in base.
 5. A method of preparing asolution as claimed in claim 4 wherein, the titanium containing compoundis water-hydrolysable and is of the formula Ti(OR)₄, where R is a C₂-C₆linear or branched chain alkyl group.
 6. A method of preparing asolution as claimed in claim 5 wherein the titanium-containing compoundis titanium tetraisopropoxide and/or titanium tetrabutoxide.
 7. A methodof preparing a solution as claimed in claim 6 wherein the titaniumcontaining compound is: first combined with a solution of oxalic acid inalcohol, followed by addition of water, or added directly to water, orto a mixture of water and an alcohol, to form a slurry, followed byaddition of oxalic acid, or added to a solution of oxalic acid in wateror in a mixture of water and alcohol.
 8. A method of preparing asolution as claimed in claim 4 wherein the titanium-containing compoundis base-hydrolysable and the titanium-containing compound is selectedfrom, but not restricted to, TiCl₄ and/or TiOSO₄.
 9. A method ofpreparing a solution as claimed in claim 8 wherein the base-hydrolysabletitanium-containing compound is hydrolysed to a hydrolysis product,using a base prior to reaction with or stabilisation by oxalic acid, thehydrolysis product being filtered and/or washed, to form a slurry beforereaction with or stabilisation by, the oxalic acid.
 10. A method ofpreparing a solution as claimed in any one of the preceding claimswherein the amount of oxalic acid is such as to provide a mole ratio ofoxalic acid:titanium in the range of about 0.2:1 to about 1:1.
 11. Amethod of preparing a solution as claimed in claim 10 wherein the watercontent of the reaction medium is such as to provide a mole ratio ofwater:titanium in the range of from about 400:1 to about 600:1.
 12. Amethod of preparing a solution as claimed in any one of claims 4 to 11wherein, when alcohol is present in the reaction medium the alcohol is amono hydroxyl aliphatic alcohol having the formula ROH, where R is a C₁to C₄ linear or branched alkyl group, such as ethanol or t-butanol, andthe preferred amount of alcohol present is such as to provide a moleratio of alcohol:titanium of between 10:1 to 50:1 in the solution.
 13. Amethod of preparing a solution as claimed in any one of the precedingclaims wherein the oxalate concentration of the solution is at any stagereduced by irradiating the solution with UV light.
 14. A solutioncontaining colloidal particles which contain titanium ions preparedsubstantially according to the method as claimed in anyone of claims 1to
 13. 15. A method of preparing a solution containing colloidalparticles which contain crystalline titanium dioxide comprising orincluding the step of: A. reacting or otherwise stabilising one or morehydrolysable titanium-containing compound(s) with oxalic acid in areaction medium.
 16. A method of preparing a solution as claimed inclaim 15 wherein A occurs under conditions such that peptization of thecolloidal solution is substantially obtained and substantiallymaintained.
 17. A method of preparing a solution as claimed in claim 16wherein the conditions include stirring or agitation of the one or morehydrolysable titanium-containing compound(s) with oxalic acid in thereaction medium, at a temperature between ambient temperature to nearthe boiling point of the reaction mixture.
 18. A method of preparing asolution as claimed in claim 17 wherein the reaction medium compriseswater or a water/alcohol mixture and wherein the titanium-containingcompound is hydrolysable in water and/or in base.
 19. A method ofpreparing a solution as claimed in claim 18 wherein, the titaniumcontaining compound is water-hydrolysable and is of the formula Ti(OR)₄,where R is a C₂-C₆ linear or branched chain alkyl group.
 20. A method ofpreparing a solution as claimed in claim 19 wherein thetitanium-containing compound is titanium tetraisopropoxide and/ortitanium tetrabutoxide.
 21. A method of preparing a solution as claimedin claim 20 wherein the titanium containing compound is: first combinedwith a solution of oxalic acid in alcohol, followed by addition ofwater, or added directly to water, or to a mixture of water and analcohol, to form a slurry, followed by addition of oxalic acid, or addedto a solution of oxalic acid in water or in a mixture of water andalcohol.
 22. A method of preparing a solution as claimed in claim 18wherein the titanium-containing compound is base-hydrolysable and thetitanium-containing compound is selected from, but not restricted to,TiCl₄ and/or TiOSO₄.
 23. A method of preparing a solution as claimed inclaim 22 wherein the base-hydrolysable titanium-containing compound ishydrolysed to a hydrolysis product, using a base prior to reaction withor stabilisation by oxalic acid, the hydrolysis product being filteredand/or washed, to form a slurry before reaction with or stabilisationby, the oxalic acid.
 24. A method of preparing a solution as claimed inany one of claims 15 to 23 wherein the amount of oxalic acid is such asto provide a mole ratio of oxalic acid:titanium in the range of about0.2:1 to about 1:1.
 25. A method of preparing a solution as claimed inclaim 24 wherein the water content of the reaction medium is such as toprovide a mole ratio of water:titanium in the range of from about 400:1to about 600:1.
 26. A method of preparing a solution as claimed in anyone of claims 15 to 25 wherein, when alcohol is present in the reactionmedium the alcohol is a mono hydroxyl aliphatic alcohol having theformula ROH, where R is a C₁ to C₄ linear or branched alkyl group, suchas ethanol or t-butanol, and the preferred amount of alcohol present issuch as to provide a mole ratio of alcohol:titanium of between 10:1 to50:1 in the solution.
 27. A method of preparing a solution as claimed inany one of claims 15 to 26 wherein the oxalate concentration of thesolution is at any stage reduced by irradiating the solution with UVlight.
 28. A solution containing colloidal particles which containcrystalline titanium dioxide prepared substantially according to themethod as claimed in anyone of claims 15 to
 27. 29. A solutioncontaining colloidal particles which contain crystalline titaniumdioxide prepared substantially as herein described with reference to anyone or more of the accompanying examples.
 30. A method of preparing aTiO₂-Containing Product comprising or including the steps of: 1)preparation of a solution containing colloidal particles which containcrystalline titanium dioxide wherein the particles are stabilised byoxalic acid or stabilised by having been reacted with oxalic acid asclaimed in any one of claims 15 to 27, and 2) preparation of a colloidalmixture by addition of, or mixing with, one or more additives to thesolution, and 3) further processing of the solution to obtain theproduct.
 31. A method of preparing a TiO₂-Containing Product as claimedin claim 30 wherein the TiO₂ phase in the product, at least initially,includes, is predominantly or is substantially anatase.
 32. A method ofpreparing a TiO₂-Containing Product as claimed in claims 30 or 31wherein the additives of step 2) include one or more of: a) silica or asilica precursor, b) water, or alcohol, soluble ketone(s), c) metalprecursor(s), d) surfactant(s), e) silane(s).
 33. A method of preparinga TiO₂-Containing Product as claimed in claim 32 wherein when silica isadded it is as colloidal silica, it is added in an amount to yield aratio substantially from 30-60 wt % relative to titanium in the product,and the concentration of the colloidal silica is such as to providebetween about 1 and 50% by weight.
 34. A method of preparing aTiO₂-Containing Product as claimed in claim 32 wherein when a metalprecursor is added, it is a metal salt or metal complex of one or moreof Pd, Pt, Ag and Cu.
 35. A method of preparing a TiO₂-ContainingProduct as claimed in claim 34 wherein the metal is Pd or Pt and theprecursor is one of the hexachloro-complexes of Pd or Pt.
 36. A methodof preparing a TiO₂-Containing Product as claimed in claim 35 whereinthe Pd or Pt hexachloro-complex is mixed with a low carbon organiccompound as a sacrificial compound, such as formaldehyde, formic acid,methanol or ethanol, the sacrificial compound added in excess relativeto the precursor metal.
 37. A method of preparing a TiO₂-ContainingProduct as claimed in claim 34 wherein the metal is Ag and the precursoris one or both of silver acetate or silver nitrate.
 38. A method ofpreparing a TiO₂-Containing Product as claimed in claim 34 wherein themetal is Cu and the precursor is one or more of copper acetate, coppersulphate and copper nitrate.
 39. A method of preparing a TiO₂-ContainingProduct as claimed in claim 32 wherein the silane(s) is added neat or assolution in an aqueous or organic solvent that is miscible with water,and is a hydrolysable or partially hydrolysable silane compound of aformula RSiX₃, R₂SiX₂ and SiX₄ (where R is a simple or functionalisedorganic group and X could be a halide or an alkoxide group).
 40. Amethod of preparing a TiO₂-Containing Product as claimed in any one ofclaims 30 to 39 wherein step 3) includes one or both the steps of: i)causing the solution to gel (a gelling step), ii) curing of the gel (acuring step) to remove or reduce the quantity of the oxalic acid and/orany one or more additives.
 41. A method of preparing a TiO₂-ContainingProduct as claimed in claim 40 wherein curing of the gel is effected byexposure to UV radiation and/or by heat, and the wavelength of the UVradiation substantially or partially coincides with the photocatalytically active band gap of the TiO₂ in the anatase phase.
 42. Amethod of preparing a TiO₂-Containing Product as claimed in any one ofclaims 30 to 41 wherein there is an additional step 4), which includesone or both the steps of: i) impregnation of the titaniumcontaining-product with a metal precursor, (an impregnation step) and/orii) transformation of any metal precursor to a metal or metal oxideadded within step 2) and/or step 4) (a transformation step).
 43. Amethod of preparing a TiO₂-Containing Product as claimed in claim 42wherein the metal of the precursor of step i) is one or more of Pd, Pt,Cu or Ag.
 44. A method of preparing a TiO₂-Containing Product as claimedin claim 42 or 43 wherein the transformation step is employed and occursby one or more of: i) heating at a suitable temperature to transform themetal precursor to the metal or metal oxide, and/or ii) exposing themetal precursor or the TiO₂-Containing Product containing the metalprecursor, to a dilute hydrazine hydrate solution for a sufficient timeto allow the complete reduction of the metal to zero valency, and/oriii) UV irradiation to form metal particles and/or metal oxides withinthe titanium dioxide.
 45. A method of preparing a TiO₂-ContainingProduct as claimed in claim 44 wherein the final metal content in theTiO₂ of the TiO₂-product is between 0.2 to 0.5% by weight.
 46. A methodof preparing a TiO₂-Containing Product as claimed in any one of claims30 to 45 wherein sometime prior to step 3) the oxalate concentration ofthe solution is reduced by irradiating the solution with UV light.
 47. Amethod as claimed in claim 46 wherein the product is a particulateproduct.
 48. A method of preparing a TiO₂ coating solution comprising orincluding the steps of: 1) preparation of a solution containingcolloidal particles which contain crystalline titanium dioxide whereinthe particles are stabilised by oxalic acid, or are stabilised by havingbeen reacted with oxalic acid as prepared in any one of claims 15 to 27,and 2) preparation of a colloidal mixture by addition of one or moreadditives to the solution.
 49. A method of preparing a coating solutionas claimed in claim 48 wherein step 2) includes any one or more of thefollowing: i) Addition of or mixing with silica, or a silica precursor,ii) Addition of or mixing with any proportion of water-soluble oralcohol-soluble ketone(s), iii) Addition of or mixing with anyproportion of surfactant(s), iv) Addition of or mixing with one or moremetal precursor(s), v) Addition of or mixing with one or more silane(s).50. A method of preparing a coating solution as claimed in claim 49wherein one or more metal precursor(s) is added or mixed and is asoluble metal salt or complex of the group of Pd, Pt, Ag and Cu.
 51. Amethod of preparing a TiO₂-coated substrate comprising or including thesteps of: I. preparation of a coating solution as claimed in any one ofclaims 48 to 50, and II. further processing of the solution to obtainthe coated substrate.
 52. A method of preparing a coated substrate asclaimed in claim 51 wherein the TiO₂ phase in the coated substrate, atleast initially, includes, is predominantly or is substantially anatase.53. A method of preparing a coated substrate as claimed in claim 52wherein the substrate is one or more of (but not restricted to) glass,quartz, glass fibre, woven glass fibre, ceramics, silicon wafers,metals, polymer surfaces (such as polyethylene or polyester), wood, orbuilding materials such as mortar, brick, tiles, or concrete.
 54. Amethod of preparing a coated substrate as claimed in claim 53 whereinstep II includes: i) application of the coating solution to a substrate,and ii) a gelling step, and iii) a curing step.
 55. A method ofpreparing a coated substrate as claimed in claim 54 wherein prior toapplication of the coating solution a protective layer of amorphoussilica and/or alumina is applied to the substrate, or a precursor ofamorphous silica selected from (but not limited to) the seriestetraalkoxysilanes, alkoxychlorosilanes; or a precursor of amorphousaluminia selected from (but not limited to) the series aluminiumtrialkoxides and wherein the precursors may convert to the silica oralumina by hydrolysis in acid solution.
 56. A method of preparing acoated substrate as claimed in any one of claims 54 to 55 wherein curingof the gel is effected by exposure to UV radiation and/or by heat andthe wavelength of the radiation substantially or partially coincideswith the photocatalytic band gap of anatase TiO₂.
 57. A method ofpreparing a coated substrate as claimed in any one of claims 51 to 56wherein there is a further step III which includes one or both the stepsof: i) impregnation of the titanium containing-product with a metalprecursor, (an impregnation step) and/or ii) transformation to a metalor metal oxide of any metal precursor added within step I) and/or stepIII) (a transformation step).
 58. A method of preparing a coatedsubstrate as claimed in claim 57 wherein the metal of the precursors ofstep i) is one or more of Pd, Pt, Cu or Ag.
 59. A method of preparing apatterned TiO₂-coated substrate comprising or including the steps of: i)preparation of a coated substrate as claimed in any one of claims 51 to58, but prior to any gelling or curing steps (if any), ii) masking oneor more regions of the coating, iii) curing of the unmasked region(s) ofcoating by exposing the unmarked region(s) to an ultraviolet light tophotocatalytically destroy the oxalic acid and other organic materialspresent in the titanium oxide of the unmasked region(s), iv) developmentof the film.
 60. A method of preparing a patterned TiO₂-coated substrateas claimed in claim 59 wherein the coating solution produces a filmwhich contains 50 to 100% by weight titania after curing.
 61. A methodof preparing a patterned TiO₂-coated substrate as claimed in claim 60wherein development of the film is by one or more of: i) application ofan acid solution wherein the acid solution is any dilute mineral acidsuch as sulphuric and/or an organic acid solution such as oxalic,lactic, citric, tartaric and/or an acidic salt solution where the saltis, ammonium sulphate or aluminium sulphate, and/or, ii) application ofother materials such as hydrogen peroxide, and/or, iii) a radiational ormechanical method including ultrasonication, and/or iv) any other methodfor redissolution of the UV—unexposed gel.
 62. A method of preparing apatterned TiO₂-coated substrate as claimed in claim 61 whereindevelopment is at room temperature.
 63. A method of preparing apatterned TiO₂-coated substrate as claimed in claim 62 wherein curing ofthe coating is by exposure to UV radiation, the wavelength of the UVradiation substantially or partially coinciding with thephotocatalytically active band gap of the TiO₂ in the anatase phase. 64.A method of preparing a patterned TiO₂-coated substrate as claimed inclaim 63 wherein there is a final step of sintering the coating.
 65. Amethod of increasing the content of rutile and/or TiO₂—B phases in aTiO₂ product including or comprising: preparing a TiO₂-containingproduct as claimed in any one of claims 30-47 wherein the TiO₂ phase ispredominantly or at least partially anatase, or is predominantly or atleast partially TiO₂—B phase and heating to increase the anatase and/orrutile content.
 66. A method as claimed in claim 65 wherein heating tosubstantially between 200° C. to 400° causes or initiates phase changeof TiO₂—B to anatase phase to titanium dioxide-B and/or rutile phase inthe product.
 67. A method as claimed in claim 65 wherein further heatingto substantially above 400° C. will increase the content of the rutilephase in the product.
 68. A method as claimed in claim 65 wherein theTiO₂ undergoes a phase change substantially entirely to rutile attemperatures substantially higher than 500° C.
 69. A method as claimedin any one of claims 65 to 68 wherein addition of substantially up to50% by weight silica results in stabilisation of the anatase phaseand/or TiO₂—B phase thereby requiring heating to over 600° C. toinitiate and/or complete the transformation to rutile phase.
 70. ATiO₂-containing product substantially prepared according to the methodas claimed in any one of claims 30-47.
 71. A TiO₂-containing productprepared substantially as herein described with reference to any one ormore of the accompanying examples.
 72. A TiO₂-containing coatingsolution substantially prepared according to the method as claimed inany one of claims 48 to
 50. 73. A TiO₂-containing coating solutionprepared substantially as herein described with reference to any one ormore of the accompanying examples.
 74. A TiO₂-containing coatedsubstrate substantially prepared according to the method as claimed inany one of claims 51 to
 64. 75. A TiO₂-containing coated substrateprepared substantially as herein described with reference to any one ormore of the accompanying examples.
 76. A method of preparing aTiO₂-based photocatalyst including or comprising the following steps: 1)preparation of a solution containing colloidal particles which containcrystalline titanium dioxide wherein the particles are stabilised byoxalic acid, or stabilised by reaction with oxalic acid as claimed inany one of claims 15 to 27, 2) further processing of the solution toobtain the photocatalyst.
 77. A method of preparing a TiO₂-basedphotocatalyst as claimed in claim 76 wherein the TiO₂-basedphotocatalyst is a TiO₂ particulate material, and the further processingincludes a gelling and a curing step.
 78. A method of preparing aTiO₂-based photocatalyst as claimed in claim 77 wherein the TiO₂-basedphotocatalyst is a TiO₂ coating or film on a substrate, and the furtherprocessing includes preparation of a coating solution, application ofthe coating solution to the substrate, and a gelling and a curing step.79. A method of preparing a TiO₂-based photocatalyst as claimed in claim77 or 78 wherein the TiO₂ phase in the particulate material, coating orfilm, at least initially, includes, is predominantly or is substantiallyanatase and/or TiO₂—B.
 80. A method of preparing a TiO₂-basedphotocatalyst as claimed in claim 79 wherein the TiO₂-basedphotocatalyst acts as a photocatalyst upon irradiation of or exposure toUV light.
 81. A method of preparing a TiO₂-based photocatalyst asclaimed in claim 80 wherein the TiO₂-based photocatalyst is metal ormetal-oxide doped, and the metal is selected from Pt, Pd, Cu or Ag. 82.A method of preparing a TiO₂-based photocatalyst as claimed in claim 79or 80 wherein the TiO₂-based photocatalyst can be used tophotocatalytically degrade organic compounds and wherein the degradationoccurs via application of or exposure to UV radiation.
 83. A method ofpreparing a TiO₂-based photocatalyst as claimed in claim 79 or 80wherein the TiO₂-based photocatalyst can act as a hydrophilic surfacewhen coated on a substrate.
 84. A TiO₂-based photocatalyst preparedsubstantially according to the method as claimed in any one of claims76-83.
 85. A TiO₂-based photocatalyst prepared substantially as hereindescribed with reference to any one or more of the examples.
 86. Amethod of preparing B phase TiO₂ including or comprising the followingsteps: 1) preparation of a solution containing colloidal particles whichcontain crystalline titanium dioxide wherein the particles arestabilised by oxalic acid, or stabilised by reaction with oxalic acid,as claimed in any one of claims 15 to 27 2) further processing of thesolution to obtain TiO₂ predominantly or substantially in the TiO₂—Bphase, 3) heating of the TiO₂ to substantially between 200-300° C.
 87. Amethod of preparing B phase TiO₂ as claimed in claim 86 wherein thefurther processing step 2) includes removal of the solvent and/or agelling step and/or a curing step.
 88. A method of preparing B phaseTiO₂ as claimed in claim 87 there is a further step 4) of heating beyond450° C. provide TiO₂ in the rutile phase.
 89. B phase TiO₂, preparedsubstantially according to the method of claims 86 to
 89. 90. B phaseTiO₂, prepared substantially as herein described with reference to anyone or more of the examples.